Many people have had the unsettling experience of their mobile app health code being of the wrong color. Now, help is on hand.

Residents can lodge an appeal and submit proofs, such as a hospital discharge certificate, if their suishenma health code shows the wrong colors, according to the Shanghai Big Data Center.

They can dial the city's service hotline 12345 or make an online appeal on the suishenban app, where they can check the reason for the red or yellow health code, said Liu Yingfeng, deputy director of the center.

Detailed and accurate documents are required for the appeal. They should submit a hospital discharge certificate, for instance, if they are classified as "confirmed or asymptomatic case", he remarked.

The big data center will work together with the city's health commission to jointly investigate all the appeals and display the correct color after verification, Liu added.

Shanghai's COVID-19 prevention authority has updated the rules to decide the health code colors.

A red code will be given to people testing positive during individual or mixed sample testing, as well as confirmed, asymptomatic or suspected COVID-19 cases and their close contacts, Liu revealed.

This list also includes overseas returnees (except those coming from Macau) and people from high-risk regions, he added.

A yellow code is for close contacts discharged from central quarantine but still under health observation as well as secondary contacts, those coming from medium-risk regions and those who failed to take part in the city's polymerase chain reaction (PCR) screening.

Those who return negative results during a COVID-19 retest will see their red code turn green immediately.